1. Field of the Invention
The present invention relates to a can and a battery using the same. More particularly, the present invention relates to a can and a battery using the same, in which a bottom wall of the can protrudes downward while forming a convex bottom surface such that the bottom wall of the can is prevented from being bent toward an inner portion of the can when the battery is compressed.
2. Description of the Prior Art
Recently, portable wireless appliances, such as video cameras, cellular phones and laptop computers, have been fabricated to be light-weight while performing various functions. This proliferation of portable wireless appliances has increased demand for secondary batteries used as power sources for the portable wireless appliances. Such secondary batteries include Ni—Cd batteries, Ni—MH batteries, Ni—Zn batteries and lithium batteries. Of particular interest are lithium secondary batteries, which are rechargeable, compact and have a high capacity. The lithium secondary batteries provide a high operational voltage and high energy density per unit weight, so they are extensively used in the advanced electronic technology fields.
FIG. 1 illustrates an exploded perspective view of a conventional lithium secondary battery. The lithium secondary battery includes an electrode assembly 112 having a positive electrode plate 113, a negative electrode plate 115 and a separator 114 in a can 110. The electrode assembly 112 is provided together with an electrolyte in the can 110 by sealing an upper opening 110a of the can 110 using a cap assembly 120.
In general, the can 110 is made from aluminum or an aluminum alloy through a deep drawing process. A bottom wall 110b of the can 110 has a substantially planar shape.
The electrode assembly 112 is formed by interposing the separator 114 between the positive and negative plates 113 and 115 and winding them into a jelly-roll structure. A positive electrode tap 116 is attached to the positive electrode plate 113 and protrudes upward out of the electrode assembly 112. A negative electrode tap 117 is attached to the negative electrode plate 115 and protrudes upward out of the electrode assembly 112. The positive electrode tap 116 is spaced apart from the negative electrode tap 117 by a predetermined distance such that they are electrically insulated from each other. In general, the positive and negative electrode taps 116 and 117 are made from Ni.
The cap assembly 120 includes a cap plate 140, an insulating plate 150, a terminal plate 160 and an electrode terminal 130. The cap assembly 120 is accommodated in an insulating case 170 and attached to the upper opening 110a of the can 110, thereby sealing the can 110.
The cap plate 140 is made from a metal plate having a size and a shape corresponding to those of the upper opening 110a of the can 110. The cap plate 140 includes a first terminal hole 141 having a predetermined size at the center of the cap plate 140. The electrode terminal 130 is inserted into the first terminal hole 141. When the electrode terminal 130 is inserted into the first terminal hole 141, a gasket tube 146 is provided around the electrode terminal 130 in order to insulate the electrode terminal 130 from the cap plate 140. An electrolyte injection hole 142 is formed at one side of the cap plate 140 with a predetermined size. After the cap assembly 120 has been assembled with the upper opening 110a of the can 110, the electrolyte is injected into the can 110 through the electrolyte injection hole 142. Then, the electrolyte injection hole 142 is sealed with a separate sealing unit (not shown).
The electrode terminal 130 is connected to the negative electrode tap 117 of the negative electrode plate 115 or the positive electrode tap 116 of the positive electrode plate 113 so that the electrode terminal 130 may serve as a negative electrode terminal or a positive electrode terminal.
The insulating plate 150 is made from an insulating material identical to the material for the gasket tube 146 and is coupled with the lower surface of the cap plate 140. The insulating plate 150 is formed with a second terminal hole 151, which is aligned corresponding to the first terminal hole 141 of the cap plate 140 and into which the electrode terminal 130 is inserted. A resting recess 152 is formed on a lower surface of the insulating plate 150, and has a size and a shape corresponding to those of the terminal plate 160 such that the terminal plate 160 can fit in the resting recess 152.
The terminal plate 160 is made from a Ni alloy and is coupled with the lower surface of the insulating plate 150. The terminal plate 160 is formed with a third terminal hole 161, which is aligned corresponding to the first terminal hole 141 of the cap plate 140 and into which the electrode terminal 130 is inserted. Since the electrode terminal 130 inserted into the first terminal hole 141 of the cap plate 140 is insulated from the terminal plate 140 by the gasket tube 146, the terminal plate 160 can be electrically connected to the electrode terminal 130 while being electrically insulated from the cap plate 140.
The negative electrode tap 117 attached to the negative electrode plate 115 is welded to one side of the terminal plate 160 and the positive electrode tap 116 attached to the positive electrode plate 113 is welded to the other side of the terminal plate 160. In order to weld the positive and negative electrode taps 116 and 117 to the terminal plate 160, a resistance welding process or a laser welding process is performed. Typically, the resistance welding process is used for welding the positive and negative electrode taps 116 and 117 to the terminal plate 160.
As the energy density of the battery increases, the size of the battery is decreased, making it more vulnerable to impact and compression. Thus, if the battery is subject to such impact or compression, the electrode assembly accommodated in the can may be deformed, thereby causing the short circuit between electrode plates and accidental ignition or explosion of the lithium battery.
In particular, as shown in FIG. 1, when the longitudinal compression test, which is one of safety tests for batteries, is performed by applying a compression force Fa, the battery is deformed about the longitudinal axis (b) thereof. As a result, the bottom wall 110b of the can 110 is bent toward the inner portion of the can 110, thereby locally compressing a lower portion of the electrode assembly, causing a short circuit between electrode plates of the electrode assembly.